The hypothalamus and limbic system are widely thought to provide the neural substrates for motivation and emotion. although the organization of its connections, and indeed the definition of what structures should even be included within the limbic system, is poorly understood and controversial. The long range goal of our work on this topic, which is now in its twentieth year of funding, is to determine with neuroanatomical methods (combined pathway tracing and histochernistry for neurotransmission-related molecules) the precise topographical organization of pathways that interconnect the various nuclei of the hypothalamus, of pathways that innervate the hy hypothalamus from medial regions of the telencephalon (such as the amygdala and hippocampus), and of pathways that descend from the hypothalamus to brainstem and spinal cord to initiate various classes of instinctive. goal-oriented behavior (e.g.. ingestive, reproductive. and defensive). Specific Aims: 1. Generate a high resolution standard map of lateral hypothalamic regionalization, based on our computer graphics atlas of the rat brain. and on neurotransmitter gene expression patterns, cytoarchitecture, and previous connectional data. 2. Determine experimentally with combined axonal tracer/in situ hybridization methods the input/output relationships of each major lateral hypothalamic region.